Heterogeneity in metal binding by individual fluorescent components in a eutrophic algae-rich lake

• Metal binding properties of individual components in NOM and algal EPS were studied.
• Six and two fluorescent peaks were respectively observed in NOM and algal EPS.
• Tyrosine- and humic-like substances in NOM and tryptophan-like substances in EPS had a higher binding ability.
• Tryptophan- and humic-like substances were responsible for Cu transportation in lakes.
• The mobility of Fe would be related to the fluorescent tyrosine-like substances.

Dissolved organic matter (DOM) affects the toxicity, mobility and bioavailability of metals in aquatic environment. In this study, the interactions between two metals of environmental concern [Cu(II) and Fe(III)] with DOM in a euthrophic algae-rich lake (Lake Taihu, China), including dissolved natural organic matter (NOM) and algal extracellular polymeric substance (EPS), were studied using fluorescence excitation–emission matrix (EEM) quenching titration combined with parallel factor (PARAFAC) analysis. Obvious protein-like peaks were detected in algal EPS matrix, while both protein- and humic-like peaks can be found in NOM. PARAFAC analysis identified four fluorescent components, including one humic-, one tryptophan- and two tyrosine-like components, from 114 EEM samples. It was shown that fluorescent tyrosine- (log KM>5.21) and humic-like substances (log KM>4.84) in NOM fraction exhibited higher metal binding capacities than those in EPS matrix, while algal EPS was characterized with a high metal-tryptophan-like substances affinity (log KM>5.08). Moreover, for the eutrophic algae-rich lakes, fluorescent tryptophan- and humic-like substances were responsible for Cu transportation, whereas the mobility of Fe would be related with the tyrosine-like substances. The results facilitate a further insight into the biogeochemical behaviors of metals in eutrophic algae-rich ecosystems as well as other related aquatic environments.